import java.util.Scanner;

public class java22
{
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int a=sc.nextInt();
        System.out.println(qiuarea(a));
    }

    public static double qiuarea(int n)
    {
        double ans=n*n*3.14;
        return  ans;
    }


}
